1. Field of the Invention
The present invention generally relates to an optical scanning device employed in an optical writing unit of a laser printer, a laser copier or the like, and deflecting a laser light emitted from a laser light source and thus scanning a surface to be scanned while forming a beam spot on the surface to be scanned, and, in particular, an optical scanning device employing a plurality of optical scanning units each including a light source, a first optical system, a deflector and a second optical system, and continuously scanning one surface to be scanned through coordinated movements of the respective optical scanning units.
2. Description of the Related Art
Recently, high density writing, high-speed writing and miniaturization are demanded for laser printers, laser copiers and so forth. Accordingly, for optical scanning devices which occupy a large space from a laser light source to a surface to be scanned, it is demanded to deal with high density writing, high-speed writing and miniaturization.
However, an optical scanning device, such as for example including a single laser light source which emits a light flux and a single deflector which deflects the light flux a surface to be scanned is scanned (raster-scanned) by means of a beam spot, and the optical scanning device needs to deflect the light flux extending from a deflector to the surface to be scanned through a wide range of the surface to be scanned. Because there is a limit to the angle by which the light flux extending from the deflector to the surface to be scanned is deflected for scanning, long distance is needed between the deflect and surface to be scanned. Thus, a large is needed in the optical scanning device. Accordingly, it is difficult to miniaturize the optical scanning device.
Further, it is necessary to reduce the diameter of a beam spot to deal with high-density writing. For this purpose, it is necessary to design the optical system subsequent to the deflector to have a small focal length. Also from this point, it is difficult to achieve high-density writing using a single laser light source and a single deflector.
An optical scanning device in the related art will now be described with reference to a figure.
FIG. 1 shows a configuration of the optical scanning device in the related art.
As shown in the figure, the optical scanning device 100 includes a light source 1 such as for example a semiconductor laser which emits a divergent laser light flux, a coupling lens 2 which is for example a collimator lens to transform the divergent light flux emitted from the light source 1 into an approximately parallel light flux, a stop 3 which reduces the diameter of the light flux made to be approximately parallel by the coupling lens 2 and cuts an unnecessary flux portion, a line-image forming optical system 4 which, as a cylindrical lens for example, has a refracting power in sub-scanning direction, and a mirror 5 which bends the light path of the light flux exiting from the line-image forming optical system 4 by reflecting it and thereby directs it to a deflection reflective surface 6a of a deflector 6. The deflector 6 deflects in a main scanning direction the light flux so as to become like a line, long in the main scanning direction by the line-image forming optical system 4 and incident on the deflection reflective surface 6a by rotating the deflector at a uniform angular velocity. An fxcex8 lens 7 corrects the light path of the light flux deflected by the deflector 6 for linearly scanning a photosensitive body 9. A long-dimensional lens 8 corrects the surface inclination of the light flux occurring from the deflection reflective surface 6a. For example, when photosensitive body 9, which is a surface to be scanned, is scanned by a beam spot formed of the deflected light flux, a synchronization detecting sensor 12 is used for establishing synchronization between the light flux emitted from the light source 1 and the rotation angle of the deflector 6 based on the incident light flux.
The light source 1, coupling lens 2, stop 3, line-image forming optical system 4 and mirror 5 constitute a scanning input optical system 15. Further, the fxcex8 lens 7 and long-dimensional lens 8 constitute a scanning and imaging optical system 18.
The optical scanning device 100 shown in FIG. 1 operates as follows:
A divergent light flux 20 emitted from the light source 1 is transformed into an approximately parallel light flux 20a by the coupling lens 2, has an unnecessary light flux portion thereof cut by the stop 3, is condensed in sub-scanning direction by the line-image forming optical system 4, is reflected by the mirror 5, and, thus, is incident on the deflection reflective surface 6a of the deflector 6 becoming like a line long in.main scanning direction.
The deflector 6 rotates at the uniform angular velocity in direction of arrow 30, and the entrance angle and exit angle of the incident light flux 20a with respect to the deflection reflective surface 6a change with the rotation of the deflector 6. Accordingly, the incident light flux 20a exits therefrom as the light flux 20bxe2x86x9220cxe2x86x9220d in the stated order as a result of being deflected by the deflection reflective surface 6a in main scanning direction according to the rotation of the deflector 6.
Each light flux 20b, 20c, 20d exiting from the deflector 6 has the light path thereof corrected by the fxcex8 lens 7 so as to scan the photosensitive body 9 linearly in direction indicated by arrow 50, and has the surface inclination of the deflection reflective surface 6a corrected by the long-dimensional lens 8.
Each light flux 20b, 20c, 20d corrected by the fxcex8 lens 7 and the long-dimensional lens 8 forms a beam spot on the-photosensitive body 9.
The synchronization detecting sensor 12 detects, for example, the light flux 20e exiting from the deflector 6, compares the timing of the thus detected light flux with the timing of the predetermined light flux emitted from the light source 1, and eliminates the difference therebetween. Thereby, synchronizes the rotational angle of the deflector 6 with the light flux emitted from the light source 1.
In order to miniaturize an optical scanning device such as that 100 shown in FIG. 1, for example, as disclosed in Japanese Laid-Open Patent Application No. 61-11720, two deflectors are used, thereby a scanning length to be scanned by each deflector is reduced, and miniaturization is achieved.
However, in such a method, as a result of two deflectors being employed, it is important to secure continuity between light fluxes (scanning laser beams) exiting from the respective deflectors, precisely. However, Japanese Laid-Open Patent Application No. 61-11720 does not clearly disclose how to secure continuity between the light fluxes precisely.
On the other hand, Japanese Laid-Open Patent Application No. 10-68899, for example, discloses a method in that two sets of deflectors and optical components for the respective deflectors are disposed stepwise, and, also, light fluxes from the respective deflators are made to be continuos by a beam splitter, and, thereby, continuity between the light fluxes is precisely secured.
However, in such a method, a beam splitter is needed as an extra component, and, also, a high level of position adjustment technology and so forth are needed for securing continuity between light fluxes from respective sets of deflectors and optical components disposed stepwise through the beam splitter.
Accordingly, it is difficult to actually manufacture it.
Further, in order to further miniaturize an optical scanning device, it is necessary to secure continuity between light fluxes from respective ones of more than two sets of deflectors and optical components through a beam splitter. However, it is further difficult to actually manufacture it because a further high level of position adjustment technology is needed.
The present invention has been devised in order to solve the above-described problems, and, an object of the present invention is to provide an optical scanning device for which miniaturization is easy, and, also, adjustment and so forth needed manufacturing it are easy.
An optical scanning device according to the present invention comprises:
a plurality of optical scanning units each comprising:
a light source emitting a light flux;
a scanning input optical system directing the light flux emitted from the light flux to a deflector;
the deflector deflecting the light flux for causing the light flux to scan a surface to be scanned; and
a scanning and imaging optical system condensing the light flux deflected by the deflector so as to form a beam spot thereof on the surface to be scanned,
wherein:
the optical scanning device scans the surface to be scanned continuously through coordinated movements of the plurality of optical scanning units; and
the respective scanning and imaging optical systems of adjacent at least two of the plurality of optical scanning units have one lens in common.
In this configuration, the optical scanning device employs the plurality of optical scanning units. Accordingly, it is possible to miniaturize the device. Further, because the lens is provided which the respective optical scanning units have in common, it is possible to provide the optical scanning device for which adjustment and so forth in manufacturing is easy.
The lens which the respective scanning and imaging optical systems have in common may comprise a plastic lens. Thereby, it is easy to form aspherical surfaces and/or free curved surfaces on the lens, and it is possible to provide inexpensive optical scanning device.
An optical scanning device according to another aspect of the present invention comprising:
a plurality of optical scanning units each comprises:
a light source emitting a light flux;
a scanning input optical system directing the light flux emitted from the light flux to a deflector;
the deflector deflecting the light flux for causing the light flux to scan a surface to be scanned; and
a scanning and imaging optical system condensing the light flux deflected by the deflector so as to form a beam spot thereof on the surface to be scanned,
wherein:
the optical scanning device scans the surface to be scanned continuously through coordinated movements of the plurality of optical scanning units; and
in order to reduce a difference between a diameter of a beam spot at a scanning end position of an optical scanning unit of the plurality of optical scanning units scanning the surface to be scanned and a diameter of a beam spot at a scanning beginning position of another optical scanning unit of the plurality of optical scanning units scanning the surface to be scanned subsequently, the respective scanning and imaging optical systems of the plurality of optical scanning units satisfy the following expression (1):
(Bn(xe2x88x92)xe2x88x92 less than B greater than )xc3x97(Bn+1(+)xe2x88x92 less than B greater than )xe2x89xa70xe2x80x83xe2x80x83(1)
where:
m: the total number of the plurality of optical scanning units;
n: any integer in the range of 1xe2x89xa6nxe2x89xa6mxe2x88x921;
Bn(xe2x88x92): a diameter of beam spot at the scanning end position of an n-th optical scanning unit of the plurality of optical scanning units;
Bn+1(+): a diameter of beam spot at the scanning beginning position of an (n+1)-th optical scanning unit of the plurality of optical scanning units; and
 less than B greater than : an average of diameters of beam-spots of the plurality of optical scanning units scanning the surface to be scanned.
In this configuration, the optical characteristics at joined portions of the respective optical scanning units are approximated by one another. Thereby, the optical scanning device is not likely to generate lines of density difference and/or the like at the joined portions only as a result of the microprocessor or the like precisely controlling switching of the outputs of the respective optical scanning units.
The scanning and imaging optical system may be approximately telecentric in main scanning direction. Thereby, shifts otherwise occurring at the joins with change in position on the photosensitive body do not occur.
An optical scanning device according to another aspect of the present invention comprises:
a plurality of optical scanning units each comprising:
a light source emitting a light flux;
a scanning input optical system directing the light flux emitted from the light flux to a deflector;
the deflector deflecting the light flux for causing the light flux to scan a surface to be scanned; and
a scanning and imaging optical system condensing the light flux deflected by the deflector so as to form a beam spot thereof on the surface to be scanned,
wherein:
the optical scanning device scans the surface to be scanned continuously through coordinated movements of the plurality of optical scanning units; and
a synchronization detecting light path for at least one optical scanning unit of the plurality of optical scanning units is provided between light paths of the respective scanning and imaging optical systems of adjacent two optical scanning units of the plurality of optical scanning units, and, also, a light directing part directing a light flux of the synchronization detecting light path to the outside of the light paths of the respective scanning and imaging optical systems is provided there.
In this configuration, even when more than two deflectors are used, it is possible to detect synchronization of the deflectors precisely.
When the synchronization detecting light path comprises a plurality of synchronization detecting light paths, the single light directing part may direct the plurality of synchronization detecting light paths. In this configuration, the synchronization detecting part may be used in common. Thereby, it is possible to save the space, to improve the space utilization efficiency, to reduce the influence of variation in characteristics of a plurality of synchronization detecting sensors, and to reduce the costs by reducing the number of synchronization detecting sensors.
An optical scanning device according to another aspect of the present invention comprises:
a plurality of optical scanning units each comprising:
a light source emitting a light flux;
a scanning input optical system directing the light flux emitted from the light flux to a deflector;
the deflector deflecting the light flux for causing the light flux to scan a surface to be scanned; and
a scanning and imaging optical system condensing the light flux deflected by the deflector so as to form a beam spot thereof on the surface to be scanned,
wherein:
the optical scanning device scans the surface to be scanned continuously through coordinated movements of the plurality of optical scanning units; and
a synchronization detecting light path for at least one optical scanning unit of the plurality of optical scanning units is provided between light paths of the respective scanning and imaging optical systems of adjacent two optical scanning units of the plurality of optical scanning units, and, also, a synchronization detecting part detecting a light flux of the synchronization detecting light path is provided there.
Also in this configuration, even when more than two deflectors are used, it is possible to detect synchronization of the deflectors precisely.
When the synchronization detecting light path comprises a plurality of synchronization detecting light paths, the single synchronization detecting part may detect light fluxes of the plurality of synchronization detecting light paths. Also in this configuration, the synchronization detecting part is used in common. Accordingly, it is possible to save the space, to improve the space utilization efficiency, to reduce the influence of variation in characteristics of a plurality of synchronization detecting sensors, and to reduce the costs by reducing the number of synchronization detecting sensors.
Further, as a result of the above-described features of the present invention being combined, it is possible to miniaturize the optical scanning device, to prevent density difference from occurring in the joints of the respective optical scanning units, and to establish synchronization of the deflectors precisely, in the optical scanning device.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.